Silica, second only to carbon black in importance among inorganic fillers in the rubber industry, can significantly improve the mechanical properties of rubber composites by optimizing its dispersibility and interfacial bonding. It is particularly effective in tensile strength, tear strength, and abrasion resistance, while maintaining the light color of the finished product.

I. Mechanical Properties of Silica
Improved Basic Mechanical Properties
Adding silica can increase the tensile strength of silicone rubber from 0.38 MPa to 16.23 MPa, an increase of 42.7 times.
In natural rubber, an appropriate proportion of silica can achieve a tensile strength of 27.6 MPa and a tear strength of 83 kN·m⁻¹.
Silica-filled rubber exhibits excellent abrasion resistance, with a DIN abrasion loss as low as 101.42 mm³.

Advantages in Dynamic Mechanical Properties
Silica-filled rubber exhibits a low Payne effect, indicating good dispersion of the filler in the rubber matrix and weak filler-filler interactions.

Adding silica can reduce the loss factor (tanδ) of rubber, especially its low tanδ around 60℃, which helps reduce rolling resistance.

Silica/carbon black blends can optimize the dynamic mechanical properties of rubber. When the mass fraction of silica in the filler is 75%, optimal tensile strength and elongation at break can be obtained by controlling the mixing time.

II. Key Factors Affecting the Mechanical Properties of Silica
Silica Particle Size and Specific Surface Area
Smaller particle sizes (e.g., 15nm, 30nm) result in a larger specific surface area of silica, a larger contact area with rubber, and a better reinforcing effect.

With the addition of coupling agent Si69, the Payne effect, loss factor, and temperature rise during constant-load compression heat generation are more significantly reduced in small-particle-size silica (15nm, 30nm). Fumed silica (specific surface area 150-380 m²/g) exhibits superior reinforcing effects compared to precipitated silica due to its smaller primary particle size (10-40 nm) and higher SiO₂ content (≥99.8%).

Surface Modification and Coupling Agent Effects:
Silane coupling agent Si69 significantly improves the dispersibility of silica in rubber, enhances the bonding between silica and the rubber matrix, and reduces the positive vulcanization time of the compound.

Ionic Liquid Modification: At a dosage of 3 phr, silica-filled natural rubber composites can increase tensile strength by up to 114%, tear strength by up to 201%, and reduce Shore Abrasion Loss (DIN) by up to 50%.

Maleamic acid (MAA): Modified silicone rubber/silica composites show increased tensile strength by 24% and 52% compared to HDMS and VTEO-modified composites, respectively, and exhibit a lower compressive stress relaxation rate.

Two-step modification: Compared to the traditional one-step method, the two-step modified silica exhibits better dispersibility in the rubber matrix and can more effectively reduce the filler network structure.

Synergistic effect of silica and carbon black: Adding a small amount of carbon black (10-20 parts) to the silica system can improve conductivity and enhance compound rigidity (↑300% elongation at a given point), while maintaining the low rolling resistance advantage of silica.

Carbon black acts as a "dispersion medium," promoting the breakup of silica agglomerates, reducing Mooney viscosity, and alleviating the problem of poor feed absorption.

When the silica/carbon black blend ratio is 30/20, the overall mechanical and dynamic mechanical properties of SSBR vulcanizates are optimal.

III. Mechanism of silica-reinforced rubber: Interfacial bonding mechanism: The silanol groups (-Si-OH) on the silica surface react with the silane coupling agent to form -Si-O-Si- chemical bonds. The other end of the coupling agent bonds with the rubber molecular chain, forming a "silica-molecular chain network structure." Ionic liquids and silica exhibit ionic dipole interactions, improving silica dispersion in natural rubber and enhancing the interfacial compatibility between rubber and fillers.

The carboxyl and amino groups of maleic acid can adhere to the silica surface via hydrogen bonds, promoting silica dispersion in silicone rubber and participating in the vulcanization reaction.
Network Structure Formation: Silica forms a three-dimensional network structure in the rubber matrix, reinforcing the rubber matrix.
Modified silica can reduce the filler network structure, decrease filler agglomeration, and improve the degree of filler dispersion in the rubber matrix.

The addition of silica helps increase the crosslinking density of rubber and enhances the bonding between rubber molecular chains.